192 .METALLUBGY OF IRON" AND STEEL.
the same weight of stone, so.that by using 500 pounds of burned, lime and 500 pounds of ore, there will be the same quantity,,of basic earth, and the same oxidizing effect, as with 1000 -pounds of raw stone, while .there will be only half as much gas produced with a contribution of 300 pounds of metallic iron.
SEC. XIc.—Use of ore with the charge.—The ore and lime are put into the furnace with the pig and scrap, so that the hearth will be protected during the. melting and an active cinder be at work continuously. When high-phosphorus stock is used, the amount of oxidation for a given weight of pig-iron is much greater than in acid practice. Thus, in 10,000 pounds of low-phosphorus iron, for an acid open hearth, the oxygen-absorbing power is as follows:
1.0 per cent. silicon=100 pounds Si, absorbing 114.3 pounds oxygen. 3.5 per cent. carbon=350 pounds C, absorbing 466.7 pounds oxygen.
Total oxygen absorption, 581.0 pounds
If pig-iron be used in basic work with the same content of .silicon and carbon, but'with the addition of 1.00 per cent., of phosphorus, there will be an additional absorptive power of 129 pounds of oxygen, or a total of 710 pounds. -With the first mixture there would be 40 per cent, of the work done during the melting (as shown in the preceding chapter), so after melting there would remain 60 per cent, of 581, or 349 pounds of oxygen to be given to the bath. In the second case., the presence of phosphorus will not cause a greater action during melting, but the absorption will be the same, so that, after melting, the phosphoric bath will have an absorptive power of 349-|-129=478 pounds of oxygen, and there will be one-third more work to do during the period of oreing. These figures explain why there is more oxidation to do with phosphoric iron than with good stock, so that it is advisable to use ore mixed with the charge to perform a part of the work during fusion. On an acid hearth ore is sometimes added with, the charge, but there is danger of this oxide uniting with the sand of the hearth. In basic practice the ore can do no harm, for it has little effect on the dolomite.
SEC. Xld.—Chemical history when no ore is mixed with the stock.—The addition of ore is not necessary .when sufficient scrap is available, for the flame will supply oxygen.to the metalloidsJas